1. Field of the Invention
The present invention relates to artificial airway devices used to facilitate lung ventilation in unconscious patients, and more specifically to devices designed for placement in the oropharynx of the patient in order to prevent airway obstruction an to permit either spontaneous or controlled ventilation.
2. Description of Related Art
To maintain open the airway of an unconscious patient under general anesthesia, it is common practice to use an endotracheal tube, which is a flexible tube of rubber or plastic which is inserted down through the trachea. Prior art endotracheal tubes frequently include an inflatable cuff around a distal end, which distal end is inserted into the trachea. The inflatable cuff is used to secure the endotracheal tube in place.
Typically, the endotracheal tube is introduced through nose and the larynx into the trachea or windpipe, and then the cuff is inflated through a small auxiliary tube in order to form a seal against the wall of the trachea. Introduction of the endotracheal tube into a patient is a skilled operation normally requiring use of a laryngoscope to guide the tube through the larynx, past the vocal cords and into the trachea. Intubation using an endotracheal tube is difficult or even impossible in some patients. Moreover, there is a significant risk of damage to soft tissues or to the larynx when using an endotracheal tube. Likewise, there is a risk of accidental, but highly undesirable, intubation of the esophagus or of the right or left main bronchus when using an endotracheal tube.
Alternatively, oro- or naso-pharyngeal airway devices may be used to maintain open the airway of a patient under general anesthesia. An oro- or naso-pharyngeal airway is a flexible tube extending from the mouth (oro-pharyngeal airway) or nose (naso-pharyngeal airway) into the patient's pharynx but not into the patient's larynx. An oro- or naso-pharyngeal airway is normally used in conjunction with a face mask over the patient's mouth and/or nose, unlike an endotracheal tube, which normally is not used with a mask. While preventing obstruction of the airway by the tongue, an oro- or naso-pharyngeal airway device cannot be used conveniently for controlled ventilation of the patient and does not prevent inhalation of extraneous matter (i.e., aspiration). For these and other reasons this type of device is less desirable in many applications.
Prior art artificial airways (see for example, U.S. Pat. Nos. 4,509,514; 4,995,388; 5,241,956; 5,249,571; 5,282,464; 5,297,547; 5,305,743; 5,355,879; 5,584,290; 5,632,271 and 5,682,880 to Archibald I. J. Brain--collectively, the "Brain patents") use a curved tube and a laryngeal mask portion at one end of the tube. The mask portion includes a flexible annular inflatable collar which surrounds a hollow interior space of the mask portion. The mask portion is pre-formed with a roughly elliptical shape which is purported to be capable of conforming to, and fitting within, the space behind the larynx to form a seal around the circumference of the laryngeal inlet without penetrating into the interior of the larynx. The curved tube opens into the mask portion and provides an airway with the axis of the tube substantially aligned with the length of the elliptical formation of the mask portion.
In the Brain patents, the curved tube opens into a lumen of the mask through an aperture which is provided with flexible cross-bars to prevent the aperture from being obstructed by the epiglottis, while permitting passage of a second smaller tube, such as an endotracheal or endobronchial tube, a suction catheter, or an inspection tube such as a fiber-optic broncho- or layrngoscope.
Even with the seal achieved by the inflatable collar in the Brain patents, there is a risk in some circumstances that if the contents of the stomach are regurgitated by the patient, the regurgitated material will travel from the esophagus and enter the bronchial tubes. The introduction of such foreign matter into the lungs, known as aspiration, is undesirable and should be avoided. Some of the Brain patents (e.g., U.S. Pat. Nos. 4,995,388; 5,241,956 and 5,632,271) attempt to solve this problem using gastric drainage features adjacent the inflatable collar.
Prior art artificial airway devices may include a drainage tube, such as those described above in certain of the Brain patents, having one end region arranged for insertion with the mask portion and the other end capable of being positioned below the patient foi extracting fluid from the area of the mask portion by siphonic action, or alternatively, the other end may be connected to an apparatus for extracting the fluid by suction. Typically, the drainage tube is of a smaller diameter than the airway tube so that the drainage tube may be accommodated within the airway tube, with the one end region opening into the lumen of the mask portion.
When the mask portion has an upstanding collar surrounding the lumen of the mask portion, the one end region of the drainage tube may be forked and adhered to the outside of the collar, with openings of the forked portions being arranged to extract fluid from the area around the exterior of the mask portion.
Alternatively, the one end region of the drainage tube may open into the esophagus when the mask portion has been inserted into the laryngeal space. For example, the one end region of the drainage tube may extend past the distal end of the mask portion so as to pass through the upper esophageal sphincter muscle. The drainage tube bifurcates at the distal end of the mask to provide fork portions lying adjacent respective lateral posterior surfaces of the flexible annular inflatable collar.